Thermionic amplifier



H. DE F. ARNOLD.' THERMIONIC AMPLIFIER. AAPPLICATION FILED JAN.8, 1920.

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Mge/#0r Hara/d //m/a/ UNITED STATES HAROLD D. ARNOLD, 0F MAPLEWOOD,

PATENT ol-"Flcr-z.V

NEW JERSEY, AssIGNoE To -wEsTEnN ELECTRIC COMPANY, INCoaPonATED, or NEW Yoax, N. Y., A coEronATIoN or NEW YORK.

THERMIONIC AMPLIFIER.

. specification of Letters Patent. 'Patented Nov. 29, 1921. Original application iled July 30, 1918, Serial No. 247,422'. Patenti-No. 1,829,283, dated January 27,l

1920. Divided and this application filed January 8, 1920. Serial No. 350,197.

ing is a full, clear, concise, and exact de scri tion.

T is invention relates to thermionicamplifiers of the electric discharge t pe and more particularly to lthose of the t ree element type', preferably highly evacuated, and

its object is to provide a structure by which certain desired characteristics of the amplifier may be secured at will and in an efiicient manner. This object is accomplished by proportioning the geometrical and electrical relations of the various elements of the device in a manner more fully explained later in this specication.

In order that the novelty of this invention may be appreciated, and that those skilled in the art may be enabled to use this` invention to best advantage, it is necessary that certain terms hereinafter used shall be defined. The following brief discussion is intended to explain the operation of the device and to define the terms to be employed.

The thermionic amplifier consists of a'container preferabl1 although not 4necessarily highly evacuate and including a hot electron-emitting cathode, such as the so-called Wehnelt. cathode, an anode and an auxiliary electrode called the grid, which vis usually, though-not always located between the anode and the cathode. A battery is connected so as to force the electrons liberated at the cathode toward the anode, thus setting up a convection current carried by electrons in the evacuated space. 'In this specification since only the structure ofthe device itself is under discussion, only theA4 effects of changes in that structure are considered. Obviously a change ir. the bat.

tery lwill also change the characteristics of the circuit, but in away which L-is already known in the art. Due to the presence of these electrons, a negative space charge is established between the anode and the cathode, whose effect is to limit the number 'of electrons which can leave the cathode, and consequently to limit .of the device.

' also the current whichcan flow in the output circuit, by which is meant the circuit includlng the battery and the path of the 4space current. The object of the grid is lto furnish a means for introducing a further negative chargeinto the space between the anodeand the cathode, or for introducing intok 1t a positive charge which shall neutralize the 'effect of part of the spaceV In the first p charge due to the electrons. case, the convection .current is decreased; in the second it is increased. In order to force this charge to the grid, a source of electromotive force is connected between grid and cathode, that is, between the input terminals The effect of such an impressed electromotive force is therefore to alter the magnitude of the space vcurrent in the amplifier by changing the .distribution of space charge between the electrodes, and moreover this is accomplished without revquiring that the impressed electromotive force shall do more work than that involved in forcing the charge to the grid againstl the counter voltage of the condenser formed by grid and filament. Since in this operation the change in power consumed in the output circuitmay, be much greater than that required in charging the condenser, the I device acts as an amplifier. This variation in space current, due to an impressed eleccromotive force, will hereafter be called the output current of the amplifier and the variation in voltage, which appears in the output circuit due `to the impressed electromotive force, will be called thevoutput voltage. The reason for adopting these definitions is that in the practical ap lications of the amplifier it is only these variations in current or voltage which are utilized; in

fact, a transformer is ordinarily used to derive ower from the output circuit, and obvious y the steady space current or the steady output voltage have no effect in the secondary of that transformer and ymay be ignored for practical purposes. Thus, the

term voltage amplification means here the ratio of the alternating voltage appearing.

in the secondary of sucha unity ratio transformer tothe alternating voltage impressed across the filament and grid, when the transformer primary is made to include whole 'of the output circuit external. to the am.

loo

Y` plier. In simpler terms, itis theratio LofV the 'bove defined output voltage to the impressed inputvvoltage.

- There will also be occasion to-,consider the ratio of voutput current to input voltag', I

' designed for given circuit'conditions so that p ao they will have whichever ofthe above mentioned characteristics is desired. That is, -pne may be designed to deliver to la receiving Idevice acomparatively high voltage'with a low current, or vice versa. The principles of operation which'have been discovered.

which enable this result to be accomplished ma be stated as follows. f' U n the first place it has been found that 1t is of advantage to locate the grid'as near the cathode as possible whatever the desired voltage amplification or output current. In practice it has been found lthat when the two elements are separated only by a mere oxidizing vcoating'the most eflicient action is obtained. Unless there isa'solid and continuous spacing-clement between the two it may be necessary of course to separate them a small distance to prevent actual contact vbetween them due to forces set up'during operation. By saying that the elements are placed as close together as possible it 1s meant that the distance between them is made as small as possible without introducing' appreciable electrical or mechanical disturbances during operation.

Again, it has been found that, when the cathode and grid are placed as near'to each other as possible, decreasing the distance from the anode to the cathode decreases the voltage amplifying power of the tube withf outat the same time reducing the variable vfirst tu current set up in the output circuit. That is, if we consider two tubes, one of which has the anode and cathode widely spaced while 7 the other has them near together, the grid being ver close to the cathode in each case, the when installed in a system of the usual kind, tends to cause marked voltage amplification, while the latter, if substituted for the former, increases the variable current output and at the saine time lowers the volta amplification.

A. ioird principle of operation of the ther mionic repeater which has been discovered may be stated as follows. To increase voltage amplification decrease the ratio of open space in the grid to conducting surface, and

l to decrease volta e amplification or to increase the variab e output current incre@ this ratio.

principl'eof operation. as follows: l mum eiliciency is obtained when'the imy70 i current control element.

`The behavior of thermionic repeatersinfv another ver important respect has been dis covered. his may 4be stated as a fourth Maxipedance Vbetween the anode and cathode isv Aequal to the total impedance of the variablecurre'nt consumption circuit. This total impedance includes the total line inipedance and that voflithe receiving or trans- -7 5 lating device or devices to which power is being supplied.

It has been found that tubes may be constructed in such manner as to take advantage,

of any number or of all of the above mentioned principles witli,l of course, correspndingly increased efficiency and yadaptabi 'ty'.

An object of the invention is to provide.

an audion, or equivalent system, by which a proper impedance ratio is lobtained-between the impedance of thatportion of the out ut 'circuit which is without-the audion and t at of the remaining pQrtion of the external circuit, whereby a giatly increased eliiciency. y

is obtained. Y

Another object of the invention is to pro? videan audion, or equivalent device, which will operateeiiiciently with a current operated translating device without the use of a voltage transformer between the audion and the translating device.

Viewed broadly, the invention proyides for an increase of the eiiiciency of an audion,

or equivalent device, by novel spacing of the electrodes and the current control element, and also an increase of' eiiiciency, 'when used with a current operated translating device, by obtaining the proper ratio of the conductive surface to open space in the Other and more specific objects-of the invention will be apparent from the appended claims.

The inventionwill be better understood by reference to the following specification taken in connection with the accompanying drawing in which- Fi re 1 represents the structure of an amplifying tube which is designed lto give cuit diagram-showing an ainplifyingsystem making use of an amplifier of the ty shown in Fig. 1. In these figures, l' e numerals represent corresponding parts.

Referring to Figs. 1 and 2, 1 represents the grid element, 2 the cathode-or filament 125 and 3 the anode or plate. Theplate is placed va considerable distance .from the cathode, and the 'd-is placed very ,close to the cathode an may be separated therefrom only by e this' insulating for iso grid or 105 example, an oxidizing .coating on one or the other. of these elements."` l Further, the grid f' is/ made to have a fine mesh and thus to obstruct greatly the view of seen from the cathode.

Fig. 3 is a diagram of an amplifying system in which a tube V of the type shown in Fig. 1 is employed. The -tube has the usual input circuit 4, and output circuit 5, 5. T he exact arrangement `of input and output cir,- cuits is that shown in Patent 1,129,942 to this applicant. In this patent there is shown and claimed a combination with another system of a system of the type sho-wn in Fig.\3, such combination having marked advantages for certain purposes specified in said patent. The purpose of the present application is to specifically describe and claim a system employing novel thermionic amplifiers, these being capable of more general use than that disclosed and claimed in the above mentioned patent..

-A source of potential 7 may be inserted in the plate as the input circuit to bring the grid to a desired initial .or working potential. No

transformer need be used, the incoming line being directly connected to the input electrodes, and the outgoing line, to the output electrodes. A high resistance element 6 may be connected across the input circuit as shown. A coil 8 of large inductance pr vides a path for direct current for the tube V, such current being supplied by a source B. The coil 8 will not conduct an appreciable amount of the variable current in the output circuitowing to its high impedance to such current. The condenser 9 is inserted in the line to prevent flow of direct current from the source B through the receiving device l0 if the latter does not itself prevent such flow.

The receiving device 10 may be one which operates most efliciently upon high variable voltage and low current. In accordance with the principles discussed above, the grid 1 and cathode 2 areplacedvery close together while the plate 3 is widely separated from thecathode, the distance between the two being that necessary to give the desired current and voltage output characteristics. It is usually necessary however forl efficient operation'to consider first the impedance characteristics of the tube between filament and plate and the impedance of the receiving device and line, in accordance with the fourth principle lof operation stated above. The receiving device 10 is one of high impedance and accordingly the impedance of the tube between filament and plate is made v high, the two impedances being made as nearly the same as'possible consistent with other possible conflicting requirements. They should at least be of the same order of magnitude, for example one being 100,000

'0111115 and the other 25,000 ohms. The reyceiving device 10 maybea second amplify;

ingZ tube or similar device. y thermionlc repeater 1s meant arepeater depending for its operation upon cur- In its 1,329,283, dated Jan. 27, 1920, of which the present application is a division.

What is claimed is:

1. A thermionic discharge device having a cathode, an anode and a controlling element, said controlling element being located in close proximityto the cathode, and said anode being relatively widely spaced from said cathode whereby the device operates to repeat electrical waves and impulses with amplified voltage.

2.-'A thermionic discharge device having a cathode, an anode and a controlling element, said controlling element being located in close proximity to the cathode, and said anode being relatively widely spaced from said controlling element whereby the device operates to repeat electrical waves and impulses with amplified voltage.

3. The combination with a thermionic discharge device having a cathode, -an anode, and an impedance varying element of an input circuit and an output circuit therefor,

means for producing a variable electromodiate proximity to the cathode, but out of" electrical contact therewith, and said cathode being widely spaced from said anode so that for the impedances and voltages employed outside the device, `the device operates to amplify the voltage of energy impressed upon said input circuit.

4. The combination with a thermionic discharge device having a cathode, an anode, and a controlling element of an input circuit therefor, and an outgoing circuit having impedance and connected to said anode and cathode, said cathode, anode and controlling element being so spaced that the impedance of said discharge device between said anode and said cathode is of the same order as that of said outgoing circuit and that said device operates as a voltage amplifier.

5. The combination with a thermionic dis-l charge device having a cathode, an anode,l and an impedance varyingelement, of an input circuit and an output circuit therefor, an impedance element in said `output circuit, means for producing a variable electromotive' force in said input circuit, and a source of electromotive force in said output cir cuit, said cathode being as near as possible to said impendance varying element and said anode bein relatively widely saced from said cathok e whereby the varia le voltage across said anode a d cathode in said output circuit is much greater than that in said input circuit.

6. The combination with a thermionic discharge device having a cathode, an` anode, and an impedance varying element, of an input circuit and an output circuit-therefor,l an impedance element in said outputv circuit, means for producing a variable electromotive force in said input circuit, and a source of electromotive force in said output circuit, said cathode being in immediate proximity to said impedance varying element,

said anode being relatively widely spaced from said cathode, and said impedance varying element being in the form of a' discontinuous conductive surface, the ratio of conductive surface to open space in said impedance varying element being high, whereby the variable voltage across said anode and cathode in said output circuit is much 'greater than that in said input circuit.

7. A thermionic discharge device having a cathode, an anode and a controlling element, said controlling element being located in close proximit to the cathode, said anodeV being relative y widely spaced from said cathode, said controlling element being in the form of a discontinuous conductive surface having a high ratio of conductive surface to. open space whereby the device operates to repeat electrical waves and imy pulses with voltage amplification.4

8. Means for amplifying' the voltage of electrical waves and impulses comprising -an electric discharge device having a` insaccati cathode, an anode', and 'a controlling element, said controlling element being located in close proximity to the cathode, said anode beingy relatively widely spaced from said cathode', an output circuit'connected to said cathode and anode, a translating device to which waves of amplified voltage are deliv- .ered connected in said output circuit,'the impedance of that portion of said output circuit which is within said discharge device being A spaced from said cathode of an input circuit connected to said impedance varying ele- -ment, a source of variable electromotive force in said input circuit, a source of electromotive force connected to sald anode and' cathode, and a work circuit non-magnetically connected to said anode and cathode, the impedance of said discharge device between said cathode and anode being of the same order as that of said work circuit.

10. Means for amplifying the voltage of electrical waves and impulses comprisin an electric discharge device having an ano e, a

` cathode, and a current control element, said current control element being located in close proximity'to the cathode, and said anode beand. said anode being re atively widely ing relatively widely spaced from said cathode, an input circuit for said device, a source ofv variable ener to beamplified connected in said input circuit, and a work circuit to which the amplified energy is delivered non-magnetically connected to said output circuit. i

In witness whereof, I hereunto subscribe my name this 7th day-.of January, A. D. 1920.

HAROLD D. ARNOLD. 

